Watermakers
are becoming more and more popular on board cruising yachts as the price
and complexity falls. We have a 12 volt electrical motorised reverse-osmosis
system called a PUR 80, designed by Recovery Engineering (based on work
to develop an energy-efficient hand-operated desalination unit that could
be operated by shipwrecked sailors). The PUR-80 produces about 12 litres
of fresh water an hour, consuming about 9 amps at 12 volts. We tend to
run it about 3 hours a day, usually when the generator is running.

The
PU 80 consists of a pre-filter (that takes out the large particles from
the seawater intake) a high-pressure pump (driven by a 12 volt motor)
and a very expensive membrane that separates the salt from the seawater.
The freshwater outflow is directed to the tanks, the (slightly salt-enriched)
waste seawater is routed overboard.

The
expensive membrane (that does the real magic work of separating
salt from seawater) is housed in a long cylindrical casing under
the saloon cabin sole.

The
high-pressure pump (driven by a 12 volt electric motor seen on the
right) is also under the floor, nearby.